High Expression of the fructose transporter GLUT5 in human breast cancer

[R.B.]

This is complex but interesting which is why I have posted it in case of interest to anybody else.

It seems to be generally accepted that cancer cells in general terms prefer to use glucose rather than 'fats' as fuel. That is a generalization as fats are metabolized in different ways depending on their structure, and there are other sugar related substances as well as glucose that are preferentially metabolized by cancer cells.

Fructose fuels similar pathways, but with important differences in the way it is metabolized. In general terms the metabolism of fructose outside the liver is limited. It is therefor fascinating that at least some lines of breast cancers appear to adapt by switching on the main fructose transport channel so they can efficiently take up fructose.

The metabolism of fructose is less regulated than glucose metabolisms - simple terms (and I struggle with all of this) there are traffic dependent stop lights for energy/fat production from glucose, but the conversion of fructose to fat and energy has a permanent green light - and the process is only stopped if the highway gets clogged with traffic.

Cancer cells need both energy to make themselves, and fats for their structure. It is more efficient for cancer cells to make some fats in situ. This saves the cancer cells the trouble of importing them. Increased energy helps cancer cells grow.

So excess fructose in the diet is probably best avoided.

http://www.ncbi.nlm.nih.gov/pmc/arti...01509-0122.pdf


"ABSTRACT The primary metabolic characteristic of malignant
cells is an increased uptake of glucose and its anaerobic
metabolism. We studied the expression and function of
the glucose transporters in human breast cancer cell lines and
analyzed their expression in normal and neoplastic primary
human breast tissue. Hexose uptake assays and immunoblotting
experiments revealed that the breast carcinoma cell lines
MCF-7 and MDA-468 express the glucose transporters
GLUT1 and GLUT2, isoforms expressed in both normal and
neoplastic breast tissue. We also found that the breast cancer
cell lines transport fructose and express the fructose transporter
GLUT5. Immunolocalization studies revealed that
GLUT5 is highly expressed in vivo in human breast cancer but
is absent in normal human breast tissue. These findings
indicate that human breast cancer cells have a specialized
capacity to transport fructose, a metabolic substrate believed
to be used by few human tissues. Identification of a highaffinity
fructose transporter on human breast cancer cells
opens opportunities to develop novel strategies for early
diagnosis and treatment of breast cancer."

[R.B.]

The arguments as to health issues surrounding fructose and its metabolism are complex.

Sucrose, table sugar is made of equal amounts of fructose and glucose.

It is pretty clear that refined fructose as HFCS or table sugar as part of a diet that exceeds the body's energy requirements is certainly a negative health factor.

Arguably refined foods generally are not optimal for health because they have been stripped of nutrients, which makes refined sweeteners a no no.

In comparison fructose in fruit comes with a whole range of protective nutrients, and as a species we have been eating it in varying quantities for a very long time. This leaves the question how much fruit and what sort is optimal to general health, and for particular conditions such as cancer.


http://www.theglobeandmail.com/life/...rticle1316253/

"However, the data showed that cancer cells used fructose and glucose in very different ways, even though they are structurally similar. Compared to glucose, fructose was a potent activator of a key cellular pathway that drives cancer cell division.

Not only did cancer cells prefer fructose, the sugar also triggered cellular activities that enabled malignant cells to use both glucose and fructose more rapidly."

[Laurel]

Ok. That WAS interesting, R.B. Thanks!